This invention relates generally to pipe cleaning processes, and more particularly to a process for cleaning and preparing the interior of a corrugated outer housing used in flexible compressed gas-insulated high-voltage transmission lines.
Compressed gas-insulated transmission lines are being increasingly utilized to transmit large magnitudes of electrical energy. Typical gas-insulated transmission lines include a cylindrical rigid outer sheath, or outer housing, typically at ground potential and a high voltage inner conductor disposed within the outer sheath. An insulating gas, such as sulfur hexafluoride, is utilized inside the outer sheath to electrically insulate the inner conductor from the outer sheath. Insulating spacers are utilized at spaced intervals along the length of the transmission line to insulatably support the inner conductor within the outer sheath.
One disadvantage with a typical gas-insulated transmission line is that the line itself is rigid; it cannot be significantly bent or turned to accommodate changes in direction or to avoid unforeseen obstacles within its path. All changes of direction in a transmission line must therefore typically be accomplished through the use of separate elements such as elbows or junction boxes. To overcome this drawback, a new type of gas-insulated transmission is to be investigated. The new type of gas-insulated transmission line utilizes a corrugated outer sheath and a flexible inner conductor to provide flexibility in the transmission line. This flexibility can then be utilized to facilitate changes of direction.
One obstacle which has been encountered in the development of such flexible gas-insulated transmission lines involves preparation of the interior surface of the corrugated aluminum enclosure. During the fabrication process and assembly of such outer corrugated enclosure, it is possible that burrs, sharp edges, and weld build-up or penetration can be present on the interior surface of the outer sheath; the presence of these abberations can enhance the electrical field during the operation of the gas-insulated transmission line, and thus cause substantial electric field problems. Furthermore, particles may be loosely adhered to the outer sheath which would subsequently become loose during operation of the transmission line and, upon becoming mobile, cause premature initiation of breakdown of the transmission line. Therefore, to avoid these problems, the interior surface of the corrugated outer sheath must be prepared and cleaned to remove these abberations.
The means utilized in the preparing and cleaning of the prior art smooth, rigid outer sheath involved the rotation of reamers with either serrated or wheel flappers. While these machines can be utilized on the smooth interior surfaces of the rigid pipe, they are inadequate for use with the corrugated outer sheath; the reamers would only contact the crowns of the corrugations, and not clean nor prepare any of the troughs of the corrugated pipe.